1. Field of the Invention
The invention relates to methods of making semiconductor devices using organic active layers. The method involves the direct deposition of patterned luminescent doped polymers by ink jet printing, and the fabrication of organic light emitting diodes (OLED's) and other semiconductor devices from ink-jet-deposited organic films.
2. Related Art
Recently, there has been increased interest in light emitting diodes made from organic polymers because of their potential low cost and potential applicability to color flat panel displays. The organic materials are typically deposited by spin-coating (in the case of polymer materials), or by evaporation (in the case of small organic molecules). In either case, the single material covers the substrate so that only devices of a single color can generally be fabricated. The straightforward integration of multiple organic layers (for the fabrication of red, green, and blue emitters for color displays) would require the patterning of the individual organic layers. Because of their solubility in and sensitivity to aqueous solutions and many solvents, such patterning of organic materials by conventional photoresist and wet processing techniques is difficult. Efforts to date to integrate organic light emitting diodes (OLED's) from materials which emit different colors on the same substrate have patterned them only indirectly (through the use of cathodes evaporated through shadow mask as dry-etch masks), or avoided the issue all together by putting the three devices on top of each other (relying on shadow masks to pattern the organics so that contacts to the multiple layers may be made).
Different colors are obtained in light emitting diodes by placing red, green and blue emitting materials in proximity to each other using photoresist patterning and etching techniques to transfer the photoresist pattern into the polymer; however, such photoresist techniques are inapplicable to organic materials because the chemicals uses for the photoresist process are incompatible with organic materials. Similarly, patterning subsequent layers on top of the organic (such as metal contacts) is difficult for the same reason. Vacuum deposited organic layers and metals may be patterned by evaporating them through shadow masks, but this technology is difficult to extend to large areas.
Other efforts using ink-jet printing in the fabrication of semiconductor devices include:
U.S. Pat. No. 4,736,704 to Henninger, deposits solder masking to a circuit board using an inkjet like technique.
U.S. Pat. No. 5,132,248 to Drummond, et al., disclose the deposition of materials on a substrate by ink-jet printing. The materials are formulated as colloidal suspensions. The materials discloses are metals, alloys, dielectrics and superconductors.
However, none of these previous efforts relate directly to the deposition of organics on a substrate by ink-jet printing.